Double patterning is employed to print features, especially those with a pitch of 72 nm or less, which is below the resolution limit of conventional lithography. However, double patterning requires at least two masks, which are expensive. To define two or more critical dimensions or pitches, at least three masks must be employed. To lower the cost of double patterning, the number of masks must be reduced.
As illustrated in FIGS. 1A through 1I, prior methods of fabricating a logic device require three or more masks to print multiple critical dimensions in the gate layer or in the active layer. Adverting to FIG. 1A, a target layer 101 is formed on a substrate 103. Target layer 101 may be the gate layer or active silicon layer. An inorganic layer 105 and an organic bottom antireflection coating (BARC) layer 107 are formed on target layer 101. Using a first mask, mandrels 109 are formed on BARC layer 107.
As illustrated in FIG. 1B, a spacer layer 111 is deposited over the entire substrate, and then etched back to form sidewall spacers 113 (shown in FIG. 1C). The width of the sidewall spacers 113 defines a first critical dimension. Adverting to FIG. 1D, the mandrels are removed and BARC layer 107 and inorganic layer 105 are etched through sidewall spacers 113. Sidewall spacers 113 are then removed, and BARC layer 107 is deposited over the entire substrate to fill the spaces between inorganic layer 105 and form a substantially planarized layer. Subsequently, a second mask is formed on BARC layer 107, exposing an area where features having a second critical dimension are to be formed. (See FIG. 1E.) As illustrated in FIG. 1F, BARC layer 107 is etched with second mask 115, thereby exposing some of inorganic layer 105 to air, and then second mask 115 is removed. As illustrated in FIG. 1G, the exposed inorganic layer 105 and remaining BARC layer 107 are then removed.
Adverting to FIG. 1H, a third mask is employed to form a structure on target layer 101 having the second critical dimension. Subsequently, as illustrated in FIG. 1I, target layer 101 is etched through inorganic layer 105 and structure 117 to form target features 119 having the first dimension and target feature 121 having the second dimension, and inorganic layer 105 and structure 117 are removed. As demonstrated, three etching steps using three masks are necessary. Further, to add target elements having a third critical dimension, but the same pitch as the first target elements, such as for a wimpy device, at least one additional mask and etching step would be required.
A need therefore exists for methodology enabling the formation of two critical dimensions or two pitches, or three critical dimensions with two pitches, while minimizing the number of masks employed.